CN109444391B - Method for measuring re-expansion rate of super absorbent resin in hardened cement slurry - Google Patents

Abstract

The invention provides a method for measuring the re-expansion rate of superabsorbent resin in hardened cement slurry. First put the container tube on the glass plate, place the single particle of superabsorbent resin in the center of the container tube, and then pour the mixed cement slurry; cover the surface of the hardened cement slurry with tape, and only expose the single particle of superabsorbent resin position; the specimen is then immersed in the test solution. The re-expansion rate of the single-particle superabsorbent resin was obtained by measuring the mass difference of the samples containing the single-particle superabsorbent resin before and after soaking, and calculating the volume increased after re-expansion. The method is simple and effective, and can be used to study the re-expansion behavior of single-particle superabsorbent resin in hardened cement slurry, and it is helpful to study the effect of cement slurry composition, environmental solution properties, single-particle superabsorbent resin type and other factors on single-particle superabsorbent The effect of resin re-expansion behavior can also be used to predict the crack healing effect of a single particle of superabsorbent resin in a certain composition of cement slurry in a specific environment.

Description

A method for measuring the re-expansion rate of superabsorbent resin in hardened cement slurry

technical field

The invention belongs to the field of cement concrete, in particular to the technical field of improving the self-healing ability of concrete by using single particle superabsorbent resin (SAP), and relates to a method for measuring the re-expansion rate of superabsorbent resin in hardened cement slurry.

Background technique

SAP can promote the self-healing of concrete cracks in water environment and high humidity environment (eg 90% humidity). When the SAP is mixed with the concrete, it absorbs the mixing water in the concrete and expands; when the concrete hardens, the SAP releases the absorbed water and shrinks, leaving initial holes in the concrete, which are equivalent to macroscopic defects. When the external load is high, cracks are generated along the SAP initial cavities. In aqueous environments, the SAP at the cracks can absorb large amounts of water, expand and plug the cracks, thereby reducing the water permeability of cracked concrete. In a high humidity environment, SAP absorbs moisture from the environment and imparts to the concrete, which can promote the hydration of the unhydrated cement and the carbonization of calcium hydroxide at the crack, generate a healing product and repair the crack.

Literature 1 (Lee, H.X.D., Wong, H.S., Buenfeld, N.R. Self-sealing of cracks inconcrete using superabsorbent polymers, Cement and Concrete Research, 2016, 79:194-208.) published a method for evaluating the healing of cracks by SAP— - Water penetration test. Split a sample with a diameter of 100mm and a height of 150mm into two parts, place a plexiglass strip of a certain width between the two parts of the sample, hoop the sample with a stainless steel ring, and obtain a crack of a certain width by adjusting the thickness of the glass strip. . The crack surface is connected to the water inlet pipe and sealed with silica gel; the other end of the water inlet pipe is connected to the water tank containing the test solution, the water tank is placed at a high place, and the height difference between the water surface in the water tank and the surface of the sample is 4m. The crack healing effect of SAP was evaluated by measuring the quality of the solution flowing through the concrete cracks.

Literature 2 (Snoeck, D., Steuperaert, S., Van Tittelboom, K., Dubruel, P., De Belie, N. Visualization of water penetration in cementitious materials with superabsorbent polymers by means of neutron radiography, Cement and Concrete Research, 2012, 42(8):1113-1121.) discloses a method for evaluating SAP healed cracks - neutron diffraction photography. The SAP-containing concrete was made into a 300×100×100mm sample with built-in reinforcement. After 7 days of curing, cracks of a certain width were made in the samples by a three-point bending test. The pre-cracked samples were dried at 50°C for 16 days, and then the crack surfaces of the samples were immersed in water to a depth of 3.5 mm. The current of the neutron beam used in the neutron diffraction photographic test is 1.5 mA. When thermal neutrons are injected into the concrete, the distribution of hydrogen atoms can be detected, and the distribution of water in the concrete can be obtained. The fracture healing effect of SAP was evaluated by the distribution of water near the fracture.

Literature 3 (Snoeck, D., Dewanckele, J., Cnudde, V., De Belie, N. X-ray computed microtomography to study autogenous healing of cementitious materials promoted by superabsorbent polymers, Cement and Concrete Composites, 2016, 65:83-93.) A method for evaluating healed cracks in SAP—X-ray tomography—is published in . The SAP-containing concrete was made into a sample with a diameter of 6 mm and a height of 10 mm. After curing for 28 days, a crack of a certain width was made in the sample through the Brazilian splitting test. Healing tests were performed after placing the specimens in different humidity environments for 28 days. X-ray tomography tests were performed before and after the healing test, and the resolution of the scanned images was 12 μm. By reconstructing the scanned image, the three-dimensional distribution of the healing products at the crack was obtained to evaluate the crack healing effect of SAP.

The shortcomings of the above technologies are that all the cracks need to be prefabricated in concrete, but the width and curvature of the cracks are difficult to control; at the same time, the process of prefabricating cracks may cause damage to SAP particles, thereby affecting the crack healing ability of SAP. In addition, the neutron diffraction photographic test requires long-term drying of the sample to drain the moisture inside the concrete; for concrete with low porosity, the drying period is longer. The processing of X-ray tomography test results is time-consuming, making it difficult to perform a large number of replicates. In addition, the key for SAP to heal cracks is that it can re-expand in cracked concrete. The above-mentioned technical operations are relatively complicated, and can only qualitatively evaluate the effect of SAP in promoting crack healing or verify the existence of healing products, and cannot obtain the power of single-particle SAP re-expansion process. Therefore, it is impossible to deeply analyze the mechanism of SAP healing cracks.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems, the purpose of the present invention is to provide a simple and easy-to-operate test method, and a method for measuring the re-expansion rate of superabsorbent resin in the hardened cement slurry that can observe the morphology during the SAP re-expansion process

The technical scheme of the present invention is as follows: a method for measuring the re-expansion rate of superabsorbent resin in hardened cement slurry. Place the cement slurry in the center of the container tube, and then pour the mixed cement slurry; cover the surface of the hardened cement slurry with adhesive tape, and only expose the SAP position; then soak the sample in the test solution, and measure the quality difference of the sample containing SAP before and after soaking , calculate the volume increased by SAP after re-expansion, thereby obtaining the re-expansion rate of SAP.

Further, the measurement method specifically includes the following steps:

S1: at first the container tube is placed on the glass plate, then the single particle super absorbent resin of a certain quality is weighed, and the single particle super absorbent resin that is weighed is placed in the center inside the container tube;

S2: pour the ready-mixed cement slurry on the surface of the single-particle superabsorbent resin of S1 to obtain a sample;

S3: The poured sample is cured for 3 days at a temperature of 18-22 degrees Celsius and a humidity of >95%;

S4: Seal the surface of the sample treated by S3 with transparent thin tape, and remove the single-particle superabsorbent resin surface tape to expose the single-particle superabsorbent resin for use;

S5: Add a small amount of deionized water to the shrunk SAP, and cover the surface of the sample with a cover plate to expand the SAP and fill its initial holes, repeat the operation to expand the SAP and fill the initial holes;

S6: After removing the cover plate, weigh the sample to obtain m ₁ , and then place the sample on the support;

S7: Put the sample and the bracket into the water tank, then add the test solution, soak it for a certain period of time, take it out, use filter paper to remove the floating water on the surface of the sample, and use an analytical balance to weigh the weight of the sample after water absorption. The re-expansion rate η is calculated by the ratio of the increased volume after water absorption by the SAP to the initial volume, and the expression of η is shown in formula (1):

In the formula: m ₀ is the initial mass (g) of the SAP particles;

m ₁ is the mass (g) of the sample containing SAP, hardened cement slurry, and hard plastic pipe before water immersion;

m ₂ is the mass (g) of the sample containing SAP, hardened cement slurry, and hard plastic pipe after immersion;

ρ _SAP is the density of SAP, which is 1.1 g/cm ³ ;

ρ _water is the density of water, which is 1 g/cm ³ .

Further, the mass of the single-particle superabsorbent resin in the S1 is 13.50-16.50 mg.

Further, the single particle superabsorbent resin includes polyacrylic acid type and acrylic acid-acrylamide cross-linked type.

Further, the container tube in the S1 is a tube body with an inner diameter of 2-6 cm and a height of more than 2 cm.

Further, the pipe body includes a polyvinyl chloride pipe, a polyethylene pipe or a polypropylene pipe.

Further, the water-cement ratio of the cement slurry in the S2 is 0.2-0.7.

Further, the test solution in S2 includes: deionized water, simulated groundwater and simulated seawater.

Further, the soaking time in the S2 is 5-100min.

Further, the cover plate is a transparent glass plate.

The key for SAP to heal cracks is that SAP can re-expand in the crack to fill its initial holes and cracks. The invention proposes a formula for calculating the re-expansion rate and a corresponding measurement method. The method is simple to operate, the morphology of SAP during the re-expansion process can be obtained, and the η value of SAP can be calculated by measuring the mass of the SAP-containing sample before and after immersion in water, so as to obtain the kinetic information of the SAP re-expansion process, which can be used to study cement slurry. The effects of mixing ratio, solution properties, SAP type and other factors on the η value of SAP provide a feasible technology for in-depth study of the mechanism of SAP healing cracks.

Features and excellent effects of the present invention are as follows:

(1) The formula for calculating the re-expansion rate of SAP in hardened cement slurry is proposed, so that the re-expansion ability of SAP can be quantitatively evaluated.

(2) The test method is simple and easy to operate, and the appearance of SAP during the re-expansion process can be observed;

(3) The properties of the cement slurry can be obtained by changing the mixing ratio of the cement slurry and the composition of the cementitious material; the properties of the solution can be controlled by changing the composition of the solution, and the type of SAP can also be changed. Therefore, this method can be used to study the effects of various factors such as cement slurry composition, solution properties, SAP type, etc. on the re-expansion rate of SAP, which is helpful to predict the fracture healing ability of SAP under different working conditions.

Description of drawings

FIG. 1 is a schematic diagram of a method for measuring the re-expansion rate of superabsorbent resin in hardened cement slurry of the present invention.

Figure 2. Schematic diagram of the mass curves of the hardened cement slurry with and without SAP removal after water absorption in deionized water (D), simulated groundwater (G) and simulated seawater (S).

Figure 3 shows the morphology of SAP in hardened cement slurry after soaking in deionized water for different times.

Figure 4 is a schematic diagram of the η value curve of SAP in hardened cement slurry after soaking in deionized water (D), simulated groundwater (G) and simulated seawater (S).

In the picture:

1. Water tank; 2. SAP; 3. Hardened cement slurry; 4. Plastic pipe;

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with specific embodiments.

The invention provides a method for measuring the re-expansion rate of superabsorbent resin in hardened cement slurry. Combined cement slurry; cover the surface of the hardened cement slurry with adhesive tape, and only expose the SAP position; then soak the sample in the test solution, and calculate the increased volume after re-expansion by measuring the mass difference of the SAP-containing sample before and after soaking. Thus, the re-expansion rate of the SAP is obtained.

The measurement method specifically includes the following steps:

S1: at first the container tube is placed on the glass plate, then a certain amount of single-particle superabsorbent resin is weighed, and the single-particle superabsorbent resin that is weighed is placed in the center inside the container tube;

S2: pour the ready-mixed cement slurry on the surface of the single-particle superabsorbent resin of S1 to obtain a sample;

S3: The poured sample is cured for 3 days at a temperature of 18-22 degrees Celsius and a humidity of >95%;

S4: Seal the surface of the sample treated by S3 with transparent thin tape, and remove the single-particle superabsorbent resin surface tape to expose the single-particle superabsorbent resin for use;

S5: Add a small amount of deionized water to the shrunk SAP, and cover the surface of the sample with a cover plate to expand the SAP and fill its initial holes, repeat the operation to expand the SAP and fill the initial holes;

S6: After removing the cover plate, weigh the sample to obtain m ₁ , and then place the sample on the support;

S7: Put the sample and the bracket into the water tank, then add the test solution, soak it for a certain period of time, take it out, use filter paper to remove the floating water on the surface of the sample, and use an analytical balance to weigh the weight of the sample after water absorption. The re-expansion rate η is calculated by the ratio of the increased volume after water absorption by the SAP to the initial volume, and the expression of η is shown in formula (1):

In the formula: m ₀ is the initial mass (g) of the SAP particles;

m ₁ is the mass (g) of the sample containing SAP, hardened cement slurry, and hard plastic pipe before water immersion;

m ₂ is the mass (g) of the sample containing SAP, hardened cement slurry, and hard plastic pipe after immersion;

ρ _SAP is the density of SAP, which is 1.1 g/cm ³ ;

ρ _water is the density of water, which is 1 g/cm ³ .

The mass of the single-particle superabsorbent resin in the S1 is 13.50-16.50 mg.

The single particle superabsorbent resin includes polyacrylic acid type and acrylic acid-acrylamide cross-linked type.

The container tube in S1 is a tube body with an inner diameter of 2-6 cm and a height of more than 2 cm.

The pipe body includes polyvinyl chloride pipe, polyethylene pipe or polypropylene pipe.

The water-cement ratio of the cement slurry in the S2 is 0.2-0.7.

The test solution in S2 includes: deionized water, simulated groundwater and simulated seawater.

The soaking time in the S2 is 5-100min.

The cover plate is a transparent glass plate.

Example 1. Measurement device

The schematic diagram of the measuring device for the re-expansion rate of superabsorbent resin in hardened cement slurry is shown in Fig. 1. The cement slurry 3 was poured on the surface of SAP 2 of known quality; after the cement slurry was hardened, the surface of the sample was sealed with tape, and only the SAP was exposed. The initial pores were filled with SAP by dropwise addition of deionized water, and the SAP-containing samples were then weighed. Invert the weighed sample and soak it in the solution for a certain period of time, then take it out, remove the floating water on the surface of the sample with filter paper, and weigh the sample containing SAP again.

Mass increase after water absorption of samples with and without SAP particles removed

The mix ratio of cement paste is shown in Table 1. The test solutions are deionized water, simulated groundwater and simulated seawater, wherein the simulated groundwater components (mmol/L): NaHCO ₃ (8.2), CaSO ₄ (1.04), MgSO ₄ (2.08) and CaCl ₂ (0.14); simulated seawater The composition is a 3.5% mass fraction of sodium chloride solution. Figure 2 shows the increased mass of hardened cement slurries with and without SAP removal after absorbing water in deionized water, simulated groundwater, and simulated seawater. The results show that the water absorption of the pre-absorbed hardened cement slurry (excluding SAP) is much lower than that of the SAP-containing hardened slurry, indicating that the weight gain of the sample during the test is mainly due to the water absorption of SAP, which also shows that this method can be used. Accurately measure the water uptake during the re-expansion process of SAP in hardened cement slurries.

The mixing ratio of cement slurry is shown in Table 1; the test solution is deionized water. The morphology of SAP after soaking for different time is shown in Figure 3.

Table 1 Cement slurry composition (g)

The η value of SAP in hardened cement slurry after soaking in different solutions is calculated according to formula (1), and the results are shown in Figure 4.

Claims (9)

1. A method for measuring the re-expansion rate of superabsorbent resin in hardened cement slurry, the measurement method is: first place the container tube on a glass plate, place a single particle of superabsorbent resin in the center of the container tube, and then pour the The mixed cement slurry; the surface of the hardened cement slurry is covered with tape, and only the position of single particle superabsorbent resin is exposed; then the sample is immersed in the test solution, and the sample containing single particle superabsorbent resin before and after soaking is measured. The quality is poor, calculate the volume increased after the re-expansion of the single-particle superabsorbent resin, thereby obtaining the re-expansion rate of the single-particle superabsorbent resin, and it is characterized in that, the measuring method specifically includes the following steps: S1: at first the container tube is placed on the glass plate, then the single particle super absorbent resin of a certain quality is weighed, and the single particle super absorbent resin that is weighed is placed in the center inside the container tube; S2: pour the ready-mixed cement slurry on the surface of the single-particle superabsorbent resin of S1 to obtain a sample; S3: The poured sample is cured for 3 days at a temperature of 18-22 degrees Celsius and a humidity of >95%; S4: Seal the surface of the sample treated by S3 with transparent thin tape, and remove the single-particle superabsorbent resin surface tape to expose the single-particle superabsorbent resin for use; S5: Add a small amount of deionized water to the shrunk SAP, and cover the surface of the sample with a glass cover plate to expand the SAP and fill its initial holes, and repeat the operation to expand the SAP and fill the initial holes; S6: After removing the cover plate, weigh the sample to obtain m ₁ , and then place the sample on the support; S7: Put the sample and the bracket into the water tank, then add the test solution, soak it for a certain period of time, take it out, remove the floating water on the surface of the sample with filter paper, and weigh the mass of the sample after water absorption with an analytical balance; the volume increased after water absorption by SAP The ratio of the initial volume to calculate the re-expansion rate η, the expression of η is shown in formula (1):

In the formula: m ₀ is the initial mass (g) of the single particle superabsorbent resin; m ₁ is the mass (g) of the sample containing single particle superabsorbent resin, hardened cement slurry, and container tube before water immersion; m ₂ is the mass (g) of the sample containing single particle superabsorbent resin, hardened cement slurry and container tube after immersion; ρ _SAP is the density of a single particle of superabsorbent resin, which is 1.1 g/cm ³ ; ρ _water is the density of water, which is 1 g/cm ³ . 2 . The measuring method according to claim 1 , wherein the mass of the single particle superabsorbent resin in the S1 is 13.50-16.50 mg. 3 . 3 . The measuring method according to claim 2 , wherein the single particle superabsorbent resin includes polyacrylic acid type and acrylic acid-acrylamide cross-linked type. 4 . 4 . The measuring method according to claim 1 , wherein the container tube in S1 is a tube body with an inner diameter of 2-6 cm and a height of more than 2 cm. 5 . 5. The measuring method according to claim 4, wherein the pipe body comprises a polyvinyl chloride pipe, a polyethylene pipe or a polypropylene pipe. 6 . The measuring method according to claim 1 , wherein the water-cement ratio of the cement slurry in the S2 is 0.2-0.7. 7 . 7. The measurement method according to claim 1, wherein the test solution in S2 comprises: deionized water, simulated groundwater and simulated seawater. 8. The measuring method according to claim 1, wherein the soaking time in the S2 is 5-100min. 9 . The measuring method according to claim 1 , wherein the cover plate is a transparent glass plate. 10 .

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